Conductive metallic powders such as those of nickel, copper, and silver are useful for internal electrodes in multi-layer ceramic capacitors; in particular, nickel powder has been recently studied for such purposes. Nickel powder produced by a dry production process is seen as being promising. In particular, an ultra fine powder having a particle size of less than 1.0 .mu.m is demanded because of requirements to form a thin layer and to have low resistance in accordance with tends toward miniaturization and larger capacity of capacitors.
As one of the process for production of the fine nickel powder, a gas phase reduction process may be mentioned. For instance, JP-A-8-246001 discloses a process in which a reactor is filled with a vapor of nickel chloride by heating and vaporizing (subliming) a solid mass of nickel chloride, hydrogen gas is supplied with an inert gas such as argon gas, and a reducing reaction occurs by contacting and mixing to form a nickel powder. According to this publication, a nickel powder having a 0.1 .mu.m to 1.0 .mu.m aver age particle size can be prepared by the process.
Although a nickel powder having a particle size within a desired range (0.1 to 1.0 .mu.m) can be obtained by the conventional process for production of a nickel powder disclosed in the above publication, it is difficult to control the required particle size more exactly within the range. To form a paste of a nickel powder, an advantageous condition includes an even and uniform particle size, a high smoothability of the particle surfaces, and a high sphericity. However, the conventional production processes cannot satisfy these conditions to a high level.
Objects of the present invention are to provide a process for production of a nickel powder, in which the particle size of the nickel powder may be freely controlled 1.0 .mu.m, especially within the range of 0.1 to 1.0 .mu.m, to improve smoothability of particle surfaces and to improve sphericity of the powder.